1. Field of the Invention
The present invention relates to the field of engine braking.
2. Description of the Background Art
Engine braking is an engine operating mode wherein the engine is reconfigured during operation to provide a braking effect to a vehicle. This may be desirable or necessary when regular wheel brakes are inadequate to provide complete braking. An example is a need for powerful and prolonged braking operations on steep grades, such as on mountain roads. Engine braking finds particular applicability on large vehicles having high wheel weights and correspondingly high momentum, and where conventional wheel brakes may fade or fail under high loading conditions or under prolonged use.
Rowells, U.S. Pat. No. 5,634,447 discloses a related art approach wherein fuel is injected during engine braking for increased braking power. Rowells, however, only addresses mass flow braking systems. Rowells injects a small quantity of fuel into the cylinders of the engine well in advance of top dead center on the compression stroke, raising cylinder pressure during compression and increasing energy to the turbocharger, inherently increasing boost pressure and braking power. Rowells therefore injects fuel to increase the turbocharger speed, which then provides more mass flow for increased braking power. Rowells does not apply to engine braking using an exhaust throttle concept, where there is very little mass flow.
One type of engine braking works by closing an exhaust throttle device in the exhaust system of the engine, thereby restricting the outflow of exhausted gases and therefore slowing the engine. This is a simple and effective way of providing additional braking power to vehicles without adding expensive and complicated devices to the valvetrain or internal structure of an engine.
A drawback of such a braking system is that internal cylinder temperatures may become very high. Excessive cylinder temperatures may be harmful to engine components. One such component is the nozzle of a fuel injector. Excessive temperatures may damage the nozzle, with a resulting degradation in engine performance.
Therefore, there remains a need in the art for improvements in engine braking systems.